So, you have contacts set to "Don't E-mail" or you're setting your newsletters to "send" with a blocking list you want filtered out so its members WON'T get the e-mail. Still, one of your contacts blocked like this receives your mail. Why could this be happening?
In this situation, it is possible that another email address is being forwarded to the customer's email in question. This is a common occurrence when someone leaves a position, and their emails are forwarded to a colleague. It can also happen after a merger or name change when old emails are rerouted to a designated recipient. Sometimes, even e-mails sent to an info@-address is directly redirected to the recipient.
If an unsubscribe link is inserted in a Newsletter, it is easy to ensure that someone is properly blocked. When the recipient or you click that link, the original recipient's email is flagged as "Don't e-mail" and they won't receive further messages.
However, if you send out using Sequences, unsubscribing will only remove the contact from that specific sequence. It will not block them from receiving other sequences they are subscribed to.
Unfortunately, it is not possible to build a mechanism to determine who has forwarded the email to the ultimate recipient as all the needed information sits on the client's side. However, you can search for the name or the domain name to identify likely possibilities, especially if the recipient themselves cannot remember which email address(es) they're is using, or if there are numerous possibilities.
